I'm concerned about the moral breakdown of the US. Historically, the US had some really strong ethical fiber, which was key to the growth of its prosperity... it was largely reinforced amongst the masses by its particular brand of religion...the vast majority had a strong desire to behave ethically. This is no longer the case...
What results is an ethical vacuum.

So the question that has been bothering me lately is this: Is it possible for a society to transition out of arbitrary-but-excellent ethics (religious guidelines) into a reason-based ethics without first going through a nasty ethical vacuum?

In a word, no.

Leftist atheists have tried this before, in the French, Bolshevik, and Nazi Revolutions, and failed horribly. Turning away from God, rejecting "square" values, promoting sodomy and discouraging traditional marriage as "freedom", taking the Lord's Prayer out of public schools, have all contributed to the mess we're now in.

To your credit, you see that we're heading downhill fast. But the only answer that's going to work is turning back to Jesus. Sorry if that's not what you wanted to hear, but it's the truth.